The present invention relates to an industrial robot designed for use in a pressing system, a pressing system, and a method of bending plate shaped material. More particularly, the invention relates to an industrial robot, a pressing system, and a method for carrying a plate shaped material, for bending the material with a press brake, and for carrying the bent material out of the press brake.
Press brakes are traditionally used for bending plate shaped material at a predetermined position and a predetermined angle. Industrial robots are also traditionally used for carrying plate shaped material in and out of the press brakes. (Japanese Pat. Laid Open No. Sho 59-175968)
The industrial robot shown in FIG. 17 has a horizontal rotary axis 103 at an upper portion of a supporting base 102. The horizontal rotary axis 103 coincides with a longer axis 101 of an upper die of the press brake. A horizontal rotary axis 105 is fixed to a leading edge portion of a squarely moving arm 104 elongated at a right angle from the horizontal rotary axis 103. A horizontal rotary axis 107 is fixed to a leading edge portion of a squarely moving arm 106 elongated at right angle from the horizontal rotary axis 105. The horizontal rotary axis 107 is the half the length of the upper die. A vertical rotary axis 108 is fixed to a leading edge portion of the horizontal rotary axis 107. A holding member 109, having plural attracting heads 110 for holding the plate shaped material, is fixed to a leading edge portion of the vertical rotary axis 108. The holding member 109 follows the plate shaped material 112 by movement of the horizontal rotary axis 103 when the material 112 is bent by raising a lower die 111 of the press brake.
In the press brake system described earlier, the holding member 109 is moved to the top surface of the piled plural material 112 by moving the horizontal rotary axes 103, 105 and 107. In this situation, the uppermost material 112 is attracted by the plural attracting heads 110 of the holding member 109. Then, the attracted material 112 is contacted with the top surface of the lower die 111 by keeping the attracting state and by again moving the horizontal rotary axes 103, 105 and 107. The lower die 111 is raised and the upper die 113 and the raised lower die 111 nip the material 112. When the material 112 is bent in the manner described above, the holding member 109 keeps hold of the material 112. Following the bending operation, the holding member 109 follows the material 112 by controlling and rotating a single axis, namely the horizontal rotary axis 103. After the bending operation is finished, the material 112 is carried to a disposing position by lowering the lower die 111 and moving the horizontal rotary axes 103, 105 and 107.
As is apparent from the foregoing, the material 112 is kept attracted by the attracting heads 110 of the holding member 109 not only when the material 112 is carried in and out of the press brake but also when the material 112 is being bent. As a result, it seems possible that shifting of the material 112 is avoided. The shifting is due to shifting of the attracting start timing to changing timing of these and other operations. Thus, the bending operation is achieved with higher precision.
The industrial robot, having the arrangement described earlier, is manufactured with the recognition that attracting the material 112 is needed not only when the material 112 is carried in and out of the press brake but also when the material 112 is being bent. It is also manufactured on the assumption that the holding member 109 follows the material 112 during bending by controlling and rotating only the horizontal rotary axis 103. In practice, it is almost impossible for the holding member 109 to perfectly follow the material 112 because the mass of the portion driven by the horizontal rotary axis 103 is extremely great. As a result, bending force is applied to the material 112. The bending force is generated by the imperfect following of the holding member 109 when the pressing processing speed of the press brake is not varied at all. This has the disadvantage of lowering the precision of the finished products. On the contrary, the holding member 109 perfectly follows the material 112 by lowering the pressing processing speed of the press brake. This inevitably gives rise to the disadvantage that the processing speed of the press brake is lowered by employing the industrial robot. More particularly, the press brake can control the bending angle by nipping the material 112 with the upper die 113 and the lower die 111 and controlling the degree of nipping. Accordingly, the nipping speed is generally kept at a constant speed. But the portion of the material 112 attached by the attracting heads 110 of the holding member 109 moves at the speed corresponding to the trigonometrical function value determined by the bending angle. The moving rate of the holding member 109 is not kept constant but is varied in correspondence with the bending angle from beginning of the bending operation to finishing of the bending operation. As a result, imperfect following of the holding member 109 is obtained under the ordinary pressing speed of the press brake because it is affected by the mass of the portion driven by the horizontal rotary axis 103. Imperfect following of the holding member 109 is also obtained because the locus of bending is not constant due to a tolerance of thickness of the material 112.
Further, a moving extent of the holding member 109 can not be determined because movability, responsibility, and physical strength of the industrial robot are greatly influenced when the moment of inertia and the like of arm members is increased too much based on increment of arm driving radius. Thus, peripheral devices for transporting plate shaped material 112 to the limit position of the holding member 109, and peripheral devices for transporting plate shaped material 112 from the limit position of the holding member 109 to the piling up position and the like are additionally required. The press brake is disadvantageously large-sized as a whole and complicated in its hardware construction and its interrelated control of each device and others.
Furthermore, as apparent from FIG. 17, the industrial robot has no degree of freedom of the holding member 109 in a width direction of the press brake. This gives rise to the disadvantage that, when the material 112 has holes at the central portion thereof, imperfect attracting of the plate shaped material 112 results due to opposition of the attracting heads 110 to the holes in the material 112.
Further, the direction of carrying the material 112 in the press brake with the industrial robot is previously determined as the front side of the press brake. Additional devices for transporting the material 112 between plural press brakes are required, thereby complicating the construction of an automated line. Also, two species of industrial robots are needed in the event that the disposition of the industrial robot relative to the press brake is on the opposite side relative to the disposition of the press brake, the disposition with other peripheral devices, or the carrying in and out position of the material 112.